Enclosures for storing electrical equipment are designed to protect the equipment from exposure to outdoor conditions. The enclosures provide protection against rain, low and high temperatures as well as impacts. In outdoor use, enclosures for enclosing electrical equipment are exposed to cyclic temperature changes between day and night. While such enclosures are designed to be waterproof, this cyclic heat load causes moisture to accumulate in the inner surfaces of the enclosure. When the temperature outside the enclosure, such as an electrical cabinet, is sufficiently much lower than the temperature within the enclosure, then there is a risk of condensation on the inner surfaces of the enclosure. Condensation will ultimately result in water to drop down onto the electrical equipment installed in the enclosure and therefore drop the maximum voltage of or damage the electrical equipment.
This issue is especially pertinent in applications where the electrical equipment inside the enclosure is switched on occasionally or cyclically. A particular example of this is a solar inverter in a photovoltaic (PV) system including a number of solar panels or modules, which operates cyclically for natural reasons. In daytime, the PV system is in operation converting solar energy from the sun for use by a utility grid. When the sun sets or when the solar panels are not able to generate enough power, the inverter is switched off completely. Further reasons for switching off the inverter include saving energy, maintenance and outages in the power grid. The cyclic operation of the inverter causes problems relating to the temperature and humidity inside the enclosure, wherein during cold periods of the diurnal rhythm, temperature inside the enclosure provides for a window of opportunity for moisture to condensate to inside the enclosure.
The condensation phenomenon may be solved by providing the enclosure with an auxiliary heater, such as a resistance thermal element, whose purpose is to maintain the inner temperature above outside temperature such that no moisture may condensate on the inner surfaces of the enclosure. However, this approach has the drawback of wasting energy, reducing the lifetime of electrical components and exposing the equipment inside to a constant heat stress which may take some components outside specification, for example, outside appropriate operating temperature range.
Another solution would be to condense the moisture with an air dryer or a Peltier element for turning the moisture into a running liquid which may be lead out of the enclosure through outlets. In outdoor use, however, such an opening in the enclosure would in the course of time accumulate undesirable growth, such as algae etc. More specifically, the outlet valve of such an arrangement would be vulnerable to the impurities of the condensed liquid. The problem of an open system is emphasized in remote locations, such as deserts and jungles. Should the problem of an open system be solved by waterproofing the enclosure, one would encounter the original problem of condensed moisture inside the hermetically closed enclosure.